When you heat olive oil at high temperatures for a long time, it makes more of two harmful chemicals—HNE and ONE—than the other oils, because olive oil is mostly made of oleic acid.

When you heat olive oil, it makes more of two harmful chemicals — HNE and ONE — than the other oils tested, likely because it’s high in oleic acid.

When you cook olive oil too hot, it starts producing chemicals that smell rancid — like old nuts or grease — and these chemicals can be used to tell if the oil has been overheated.

When olive oil gets really hot, one of its healthy compounds — hydroxytyrosol acetate — goes up, which might be a clue that the oil has been overheated.

Olive oil from Al-Jouf stays fresher longer than olive oil from Pakistan when left out at room temperature, based on how quickly it breaks down.

Scientists can estimate how long it takes for half of the healthy compounds in olive oil to break down when it’s heated at different temperatures.